What aspects of Karim and Changez make them character foils of one another and likely allow for their strong friendship?

Karim and Changez have different character strengths, but similar character faults. They are both skilled at observing others, but continually fail to recognize their own deficiencies. Changez is physically stunted and Karim, though maturing, remains emotionally stunted. These similarities form the basis for a strong friendship that weathers Karim's betrayals of Changez